1. Field of the Invention
The present invention pertains to orthodontic appliances for correcting teeth malalignment. Specifically, it pertains to an orthodontic bracket for use in combination with arch wires in edgewise appliances.
2. Brief Description of the Prior Art
For many years the most popular, effective, and mechanically sound orthodontic appliances used in correcting imperfections in the alignment of teeth has been the appliance generally referred to as the "edgewise appliance". Although there are several variations of the edgewise appliance, it normally comprises brackets which are attached to each tooth and at least one arch wire which spans the teeth engaging each of the brackets. The arch wire may be affixed to each bracket by connecting wire, resilient band or the like. Examples of various types of brackets may be seen in U.S. Pat. Nos. 3,043,007; 3,193,930; 3,626,593; 4,242,085 and 4,310,306.
Most edgewise brackets include a base portion which is adapted for attachment to the outer surface of the tooth, a rectangular groove or slot for receiving the arch wire and wing portions on each side of the slot so as to provide a means of tying or holding the arch wire in place. The width of the bracket slot is very accurately formed to receive the normal rectangularly cross-sectioned wire in a very precise fit. With such attachment, it is possible to control the inclination of the teeth in three planes of space.
For many years, the width of the slot in edgewise brackets was designed for receiving an arch wire, the cross-sectional height of which was 0.022 of an inch. Such a wire is relatively stiff and exerts an often unnecessary amount of force on the teeth. Consequently, many orthodontists began using edgewise appliances with slots designed to receive arch wires having a height of 0.018 of an inch. Through years of use, it became apparent that the larger dimensioned brackets, when used with small wires, had several advantages: greater range and resiliency of the wires used, and less permanent deformation of the arch wires due to occlusive forces during mastication. However, the loose fit between a larger dimensioned bracket and a small wire results in reduced control of the teeth in certain areas.
In early or intermediate stages of straightening a patient's teeth, it may be desirable, for some of the teeth, to have limited freedom of movement (i.e. a loose fit between the bracket and wire). Consequently, some orthodontists use the large slot bracket (0.022") and the smaller dimensioned arch wire (0.018"). The loose fit between the smaller dimensioned wire and the larger dimensioned bracket allows the wires to work over a longer period of time, imparting less force. This speeds up the leveling stage of treatment and reduces the number of wires used during treatment. In addition, such a loose fit minimizes the problem of the wires being deformed during mastication. While the loose fit between the smaller wire and the larger appliance is desirable in some situations, it is undesirable in others. As earlier mentioned, the loose fit sacrifices control. In the past, orthodontists were forced to choose between a close fit between the bracket and wire or a loose fit using the larger slot with a smaller wire, losing certain advantages regardless of the choice.
Clinical use has demonstrated that the most efficient appliance would be one which used brackets of at least two different sized slots. Brackets with the smaller dimensioned slots would be attached to the anterior or front teeth and brackets with larger dimensioned slots would be attached to the posterior or back teeth. Thus, the advantages of a loose fit would be provided in the posterior part of the mouth and the advantages of greater control (where it is more needed) would be in the anterior part of the mouth. While this may provide the greatest flexibility in treatment of the anterior and posterior teeth and while it may be the best appliance configuration of the prior art, it still does not offer tight fit/loose fit flexibility for treatment of a particular tooth unless the brackets are changed.